The present invention generally relates to a liquid crystal optical switching device and, in particular, relates to one such switching device having such port thereof including means, extending toward a liquid crystal material, for receiving an optical fiber.
The use of optical fibers as a telecommunication transmission medium has numerous advantages compared to existing telecommunication transmission media. For example, optical fibers can sustain signals having wider bandwidths and hence can convey larger quantities of information than existing media. Further, light waves are shorter than the conventional microwaves currently used in many existing telecommunications systems and thus a substantial reduction in the physical size of components is readily achievable. This size reduction further results in cost reductions for materials, packages and manufacturing. Still further, current optical fibers exhibit little or no electromagnetic radiation or radio frequency radiation, thus resulting in little or no impact on the surrounding environment.
To be viable, however, every telecommunication system must include some means for controllably redirecting a signal, or a portion thereof, to or from a transmission medium, or between one or more such media. In the case of an optical telecommunication system, the means is an optical switch. Conventionally, the majority of optical switches have been mechanical although recently liquid crystal switches have been proposed.
In general, mechanical switches require relatively high driving power and are subject to wear, abrasion and fatigue. Further, mechanical switches are prone to failure after repeated use. In addition, since a rather small optical fiber is usually displaced from alignment with a first port fiber to alignment with another port fiber, mechanical switches are expensive, due to the very small tolerances allowed to ensure the proper alignments.
Advantageously, a liquid crystal optical switching device has no moving parts and is thus free from many of the drawbacks of mechanical switches. Proposed liquid crystal optical switches have been described in U.S. Pat. No. 4,201,442 issued to McMahon et al. on May 6, 1980, U.S. Pat. No. 4,278,327 issued to McMahon et al. on July 14, 1981; and U.S. Pat. No. 4,385,799 issued to Soref on May 31, 1983. Therein, liquid crystal switches are described having optical fibers attached to the side angled surfaces of a pair of trapezoidal prisms. The trapezoidal prisms are arranged with the bases thereof parallel and liquid crystal material is positioned therebetween.
Although the optical switches described by these references have some advantages over mechanical switches, i.e. no moving parts, these liquid crystal switches are both expensive and quite difficult to mass produce.
Specifically, each set of trapezoidal prisms must be precisely matched to ensure the exactness of the optical path, the trapezoidal prisms must also be optically flat to avoid detrimental light scattering at the surface and, in addition, must be optically pure to avoid internal light scattering. Light scattering and optical path inaccurancy can result in both signal loss and crosstalk. Further, to manufacture such a switch each optical fiber must be attached precisely perpendicularly to the angled surface of the trapezoidal prism to avoid surface reflections and diffraction. Still further, the trapezoidal prisms must be precisely aligned to each other to avoid signal losses. In addition, the location of the optical fibers on the prism surfaces is critical to avoid substantial signal losses caused by misalignments. As a result, the optical switches described in these references are quite impractical for optical communication systems.
Consequently, since a typical telecommunication network may include hundreds, if not thousands, of switching devices, a low cost, easily mass produced optical switching device is needed in order to fully realize the advantages of an optical telecommunication system.